This week mathematical enthusiasts around the world recognized June 28th as National Tau day. While March 14th (3/14) has long been acknowledged as Pi Day due to its numerical resemblance to the first three numbers in the decimal expansion of pi, proponents of tau insist the holiday be more appropriately referred to as “Half Tau Day.”
Tau advocates, or Tauists, assert that tau equals approximately 6.28, which is twice as much as pi, and therefore believe that the number itself is more significant than pi alone. Efforts to replace pi with tau have been ongoing for about ten years but it was Michael Hartl who brought widespread attention to the movement in June 2010. In “The Tau Manifesto,” a dedication to one of the most notable numbers in math, Hartl explains that pi is not factually incorrect, however, it is a “confusing and unnatural choice for the circle constant.” Pi is the ratio of circumference to diameter of a circle but tau is circumference divided by radius. Simple enough, right?